This invention relates to rotary dynamoelectric machines of the brushless direct current motor type having a disk configuration, and in particular relates to improvements in stators for that kind of machine.
For a brushless DC disk motor, which generally comprises sets of adjacent magnetisable disks bearing a plurality of interacting magnetic poles and one disk is caused to rotate about an axis as a result of torques produced by interaction between fixed magnetic poles in usually the movable surface or rotor, and windings for generating controllable magnetic poles within usually the fixed surface or stator (so that no wiping commutator is required), there is generally a need to construct motors that are as efficient as possible. (Of course the same argument could be used for a dynamo in which case the device is instead a transducer to convert motive power into electrical energy, and this document includes dynamos within its scope).
Stator design involves consideration of the magnetic circuit and where ferromagnetic elements of high magnetic permeability (including, of course, the permanent magnets) are involved it is useful to minimise the portions of any magnetic circuit that have a low permeability. As a result a given current within any winding results in a greater torque (or vice versa for a dynamo). The present application explores ways to improve the design of wound stators which are primarily applicable to cases where windings associated with a disk form include a large radially directed amount of conductor, such as in a disk motor.
It is an object of this invention to provide an improved rotary dynamoelectric machine, or at least to provide the public with a useful choice.
In one aspect the invention provides a stator winding for a discoidal rotary dynamoelectric machine, having a plurality of generally radially disposed groups of conductors; wherein the space occupied by the conductors of any one group is wider (from side to side) and shallower towards the periphery of the stator and narrower (from side to side) and deeper towards the center of the stator.
In another aspect the invention provides a discoidal rotary dynamoelectric machine, having at least a rotor disk and a stator disk supporting a stator winding as described in the previous paragraph
Preferably each group of conductors on the stator lies over a ferromagnetic malarial having a magnetic permeability greater than that of air.
Preferably the cross-sectional area of each group of conductors is substantially constant at any plane tangential to the axes of rotation and including the radially disposed groups of conductors.
Preferably the ferromagnetic material slopes away from the rotor from the periphery of the stator towards the center of the stator, so that the ferromagnetic material is maintained adjacent to the windings.
Preferably the ferromagnetic material is chosen from the group comprising: iron wire, iron strip, iron powder, and bulk iron.
Preferably the stator is a shaped disk and has a plurality of generally radially disposed depressions capable of receiving a plurality of tins of the conductors, wherein each depression is wider towards the periphery of the disk.
Preferably each depression is also deeper towards the center of the shaped disk.
Preferably the rotor has between two and 128 permanent magnetic poles, and in its most preferred form has 8 poles.
In another aspect the invention provides a method of creating a stator winding for a discoidal rotary dynamoelectric machine, by winding a plurality of generally radially disposed groups of elongate conductors on a shaped former having a center and a periphery, the shaped former has a plurality of generally radially disposed depressions capable of receiving a plurality of turns of the conductors, wherein each depression is wider towards the periphery and conductors are wound in such a way that the space occupied by the conductors of any one group is wider (from side to side) and shallower towards the periphery of the stator and narrower (from side to side) and deeper towards the center of the former.
In a further aspect this invention provides a rotary dynamoelectric machine, having at least a first and a second adjacent magnetisable surface each in the form of a disk and each bearing a plurality of magnetic poles, where one surface may be caused to rotate, about an axis, across the other surface as a result of interaction between fixed magnetic poles included in the first surface and controllable magnetic poles included in the second surface, wherein the magnetic poles of at least one second surface result from electric currents flowing within a plurality of groups of wound conductors or windings, each group being wound within a depression formed within a shaped disk, each depression being expanded laterally towards the periphery.
Preferably each depression lies over a ferromagnetic material (having a magnetic permeability greater than that of air), forming part of a magnetic circuit including the adjacent first surface.
It is also preferred that each depression is also deeper towards the center of the shaped disk.
Preferably each depression is deeper towards the center of the shaped disk, so that the cross-sectional area in a tangential plane to the axis of rotation of the second surface and including a winding area is substantially similar.
Preferably the maximum number of turns of conductor that can be wound so as to lie beneath the outer boundaries of the depression is substantially constant at any plane tangential to the axis of rotation and including a winding areand
Preferably the ferromagnetic material is also positioned deeper towards the center of the shaped disk, so that the ferromagnetic material is maintained adjacent to the windings.
Ferromagnetic materials can include: iron wire or iron strip wound in the form of a watch-spring coil, possibly a ferrite, iron powder, or for dynamoelectric machines intended for use at relatively low speeds, bulk iron.
A preferred ferromagnetic material is a magnetically soft iron wire wound in the form of a coil
Another preferred ferromagnetic material is a magnetically soft iron strip wound in the form of a watch-spring coil.
Yet another preferred ferromagnetic material is iron powder, either pressed into the required shape or supported by epoxy/plastic binders.
An alternative ferromagnetic material, more particularly for dynamoelectric machines intended for use at relatively low speeds, is bulk iron or more preferably an alloy including iron and having a relatively low hysteresis.
A preferred number of poles is between two and 128.
More preferably the number of poles is eight.
In another aspect the invention provides an electric disk motor, having a magnetisable assembly facing an array of generally radially oriented windings; one being rotatable in relation to the other, one having magnetic poles, the other having windings, the windings being held within cavities in a support structure, wherein each cavity is wider and shallower towards the external periphery of the motor and narrower and deeper towards the center of the motor.
In another aspect the invention provides a brushless DC disk motor, having a rotatable permanent magnet assembly and an array of generally radially oriented windings in more than one sector each held within a corresponding slot in a shaped winding former, wherein each slot provides a winding space, and wherein the space occupied by the winding of any one sector is wider and shallower towards the periphery and narrower (from side to side) and deeper towards the center of the moulded winding former.
The invention also encompasses a stator or a shaped winding former for such dynamoelectric machines (particularly for brushless DC disk motors).
In a further broad aspect the dynamoelectric machine may be operated in a dynamo mode of operation, in which causing relative rotatory motion of the first and second disks has the effect of inducing the flow of electric currents within the plurality of groups of wound conductors.
The dynamoelectric machine can have at least one stationary disk including windings and hence no wiping contacts capable of carrying current between a fixed conductor and a rotating conductor.
Alternatively the at least one stationary disk includes permanent magnets, and wiping contacts capable of carrying current between a fixed conductor and a rotating conductor are provided in order to energise windings on at least one rotatable disk.
The description of the invention to be provided herein is given purely by way of example and, together with the various examples to be described and illustrated, is not in any way to be taken as limiting the scope or extent of the invention. It should also be recognised that some of the drawings include dimensions in millimetres to aid in the understanding of the shape of the stator, but such dimensions are given purely by way of example and are not intended to be limiting in any way.